The present invention relates to a rotary joint for optical fibers conveniently used on winding drums for a composite cable which connects the mother ship and the machines for underwater operations.
The optical communication technique using optical fibers has recently shown a remarkable progress and it has been put to practical applications in various fields. As an example of such uses, there is a signal transmission means to transmit signals in the composite cable 3 which connects the mother ship 1 and the machine 2 for underwater operations with the power supplied from the ship 1 (FIG. 1). The composite cable 3 consists of a power transmission line, a signal transmission line and a tension member. Introduction of optical transmission system using optical fibers would eliminate the influence of electromagnetic induction from the power transmission line heretofore encountered in the electrical transmission system. The optical system would also reduce the mechanical impact on the machine 2 for underwater operations as the composite cable 3 can be reduced in its diameter and weight. Further, the system has a wider frequency band which is necessary for transmitting picture signals. There are however several technical inadequacies at present as to the use of optical fibers in composite cable 3. For example, no rotary joint for optical fibers has yet been developed. The composite cable must be wound in and out each time the mother ship moves during underwater oprations, and for this reason, the composite cable is usually wound by means of a drum which is easier to handle. The power or signal is transmitted via a slip ring which rotates interlockingly with the drum between the composite cable at the mother ship and the composite cable in the water. In the case of a composite cable using the optical fiber transmission system, since no rotary joint for optical fibers usable as a counterpart of the electrical slip ring has been developed, the optical signals must first be converted to electric signals to be passed through the slip ring before converted to optical once again. However, the electromagnetic induction from the power transmission line tends to affect as the signals are converted to electric signals in this system. And moreover, when the frequency band of the signals is wider, a special slip ring must be used. These defects offset the features of optical fibers.